1. Field of the Invention
The present invention relates to feedthrough devices.
2. Related Art
Historically, feedthrough devices were widely used in vacuum technology allowing for the transfer of signals between chambers of differing pressures. In such applications, the vacuum tubes had to be sealed because they could only operate under low pressure conditions. In the early feedthrough devices, such as those used for vacuum tubes, the feedthroughs were essentially made from glass plugs which were partly melted to allow electrical conductors to be passed therethrough.
Over time, other devices have also required a mechanism of allowing electrical connections between hermetically sealed circuitry and an external device, such as those devices that are used in medical implants to provide therapy to a patient, such as cardiac pacemakers, defibrillators and cochlear implants. As the environment of living tissue and body fluids is quite corrosive and the implants may contain materials which may be detrimental to the patient, a hermetic feedthrough device is used to provide a barrier between the devices electronics and the external corrosive environment of the human body.
One example of a feedthrough developed for use in medical devices is shown in U.S. Pat. No. 4,678,868. The '868 patent describes an alumina insulator to provide hermetic sealing and electrical isolation of a niobium conductor pin from a metal case. Other typical feedthrough devices utilize a conductive pin to provide a conductive path through the feedthrough and also include a ferrule which permits attachment of the feedthrough to the case. The conductive pin and a hermetic glass or ceramic seal which supports the pin within the ferrule and isolates the pin from the metal casing. However, these types of feedthroughs have generally been not acceptable for use in medical implant applications because of the likelihood of corrosion and deterioration.
Other materials and processes are known for making feedthroughs, for example, from aluminum oxide ceramic and binders. These types of feedthroughs are widely used for cardiac and cochlear implants. One of the processes for making such a feedthrough consists of pre-drilling holes in a sintered ceramic plate and then forcing electrical conductive pins through the holes. However, this method does not necessarily guarantee a hermetic seal. A second method involves inserting the conductive pins into an unsintered (or “green”) ceramic plate and then curing the assembly by firing to achieve a hermetic seal. A major disadvantage of this last method is that, historically this has been performed by hand. Such a method of manufacture can lead to inaccuracies and be time consuming, expensive and labor intensive. Moreover, the feedthrough devices resulting from such a process do not necessarily have precisely positioned electrical conductors. The position of the conductors being greatly dependent upon the process itself.